Pickup box bolt-up problem

[jon75]

When I purchased my 1975 GMC, the box had been swapped years before with a 1986 Chevrolet box. My issue is that the second set of bolts from the front do not line up with my frame holes. There are holes there but they seem to conflict with the front upper mount for the leaf springs.

With the leaf springs, exhaust, and driveshaft in there, it's kind of hard to get my head up in there to see what the clearance looks like. I am not sure if the bolts are different length in this location or not.

Between the two forward bolt holes in the bed are a set of bosses where they may have made holes in the old beds. The frame directly below these bosses have holes that look like they used to have bolts in them. So I am thinking that this is where the old bed bolted down, but I'm not sure.

I would like to know if all of this information is true...

If it is, what would you guys recommend I do? I can either drill out the forward holes (but that would leave the holes behind it exposed) or I can try and figure out how to get some bolts in the existing holes. Let me know what you think.

(sorry I don't have any pictures to show you)